For the treatment of a patient suffering from renal failure, there have been proposed various blood purifying methods in which blood is taken out from the body of the patient to be purified and is returned into the body. To purify the blood, hemodialyzers which accommodate a porous membrane (hereinafter also referred to as “dialysis membrane”) such as a hollow yarn cellulose membrane, polyacrylonitrile membrane or polysulfone membrane in the housing are generally used. The purification method to be employed differs according to the state of the disease and the conditions of a patient.
For example, in the case of hemodialysis (HD), blood and a dialysis fluid are contacted with each other through the dialysis membrane of a hemodialyzer to remove urotoxin such as urea and uric acid accumulated in the blood of a patient by the movement of substances caused by diffusion. In the case of hemofiltration (HF), water, body wastes and toxins contained in the blood are removed by filtration through holes open in a porous membrane.
In the above treatment method, HD (hemodialysis) is excellent in the removal of small-molecular wastes and solutes but is inferior in the removal of medium molecules and large molecules. Therefore, it is known that when HD is continued for a longtime, the development of a complication such as secondary dialysis-related amyloidosis or trophopathy cannot be suppressed. Meanwhile, HF (hemofiltration) is excellent in the removal of medium and large molecular wastes but is inferior in the removal of small molecules. Therefore, it is considered as unsuitable for long-term treatment since toxin such as urea is accumulated in the body.
As a treatment method having the advantages of both HD and HF, that is, well-balanced removal efficiency for small to large molecules, there has been proposed hemodiafiltration (HDF). However, since filtration and fluid substitution operations have been complicated in the clinical scene and restrictions have been placed on the use of a bottle preparation of an expensive substitution fluid by medical economy, a small amount, for example, 5 to 10 liters of a substitution fluid has been used. Therefore, the excellent removal characteristics of HDF could not be obtained fully and a marked clinical effect did not appear. Recently, to eliminate a shortage of a substitution fluid, on-line HDF method in the broad sense which is a new technique capable of large-quantity filtration and large-quantity fluid substitution has been established by using a purified dialysis fluid as a substitution fluid for filtration. The technology as shown, for example, by JP-A 6-134031 and JP-A 7-313589 as prior art documents is disclosed.
HD, HF and HDF are treatment methods making use of a removing apparatus which is installed halfway in extracorporeal circulation, for taking out the blood of a patient to the outside of the patient's body and recirculating it into the body. Therefore, to maintain extracorporeal circulation, an extracorporeal circulation circuit (also referred to as “blood circuit”) is used, one end of the blood circuit is connected to a puncture needle on the arterial side which is introduced into the blood vessel of a patient to extract the blood (blood extraction), and the other end of the blood circuit is connected to a puncture needle on the venous side which is introduced into the blood vessel of the patient to return the blood into the body of the patient (blood reinfusion). That is, blood access operation for introducing the two puncture needles is required to maintain extracorporeal circulation.
However, since the blood vessel is thin and fragile, there is a case where it is difficult to leave the two indwelling needles on the arterial and venous sides. In the current situation where the number of old dialysis patients is increasing, the number of cases where this blood access is difficult is increasing each year. For the cases where blood access is difficult, so-called “single-needle HD” in which the extraction of the blood from a patient and the reinfusion of the blood to the patient from the blood circuit are carried out with a single needle alternately and intermittently may be carried out. However, conventional single-needle HD is unsuitable for the long-term treatment of a patient suffering from chronic renal failure as its removal efficiency for urotoxin is extremely low.
The present invention provides a novel single-needle hemodiafiltration apparatus (hereinafter also referred to as “single-needle HDF”) which shows a well-balanced excellent removal efficiency for from small to large molecules and realizes the purification of blood by single-needle extracorporeal circulation.